Separating system for carpeted floor

ABSTRACT

Comminuted carpet pieces are fed to a first stirred tank together with an aqueous solution containing separating salt, to form a first suspension, which is fed to a first mechanical separating stage. A first high-solids phase, a second high-solids phase containing polymer fiber material, and a liquid phase are obtained therefrom. The second high-solids phase is mixed with a water-containing separation solution in a stirred tank, to give a second suspension, which is fed to a second mechanical separating stage. A third high-solids phase, a polymer fiber material-rich phase and a liquid phase are withdrawn therefrom. An acid which is stronger than H 2 CO 3  is introduced into the stirred tank together with the water-containing separation solution, and the pH of the liquid in the stirred tank is adjusted to 2-6.

[0001] The invention relates to a process for separating polymer fibermaterial from comminuted carpet pieces, which are fed to a first stirredtank together with an aqueous solution containing separating salt, and afirst suspension is withdrawn from the first stirred tank and fed to afirst mechanical separating stage, from which a first high-solids phase,a second high-solids phase containing polymer fiber material, and aliquid phase are separated off, the second high-solids phase being mixedwith a water-containing separation solution in a second stirred tank,and a second suspension being withdrawn from the second stirred tank andfed to a second mechanical separating stage, from which a thirdhigh-solids phase, a polymer fiber material-rich phase, and a liquidphase are separated off.

[0002] A process of this type is disclosed in EP 0681 896 B1. In thisprocess, the carpet is wet-ground in two stages and separated into threefractions in two centrifuge separating stages connected in series.

[0003] The invention is based on the object of improving the knownprocess and obtaining polymer fiber material, for example polyamidefibers, in the highest possible purity in an inexpensive manner. This isachieved in accordance with the invention in the process mentioned atthe outset in that an acid which is stronger than H₂CO₃ is introducedinto the second stirred tank together with the water-containingseparation solution, and the pH of the liquid in the second stirred tankis adjusted to 2-6. Due to the acidification in the second stirred tank,residues of chalk are dissolved and can be separated off completely.Chalk-containing particles, in particular rubber particles, lower theirspecific gravity due to the dissolution of the chalk and can bedischarged with the third high-solids phase through the mechanicalseparating stage. Suitable acids which are stronger than H₂CO₃ are, forexample, nitric acid, hydrochloric acid, acetic acid or formic acid.

[0004] The separating salt fed to the first stirred tank isadvantageously a calcium salt which is readily soluble in water andwhose acid dissolves calcium carbonate. Suitable calcium salts are, forexample, calcium nitrate and calcium chloride. However, it isalternatively also possible to use a readily soluble salt such as, forexample, K₂CO₃.

[0005] One or both separating stages preferably operate with adouble-cone full-jacket centrifuge. Before each centrifuge, a suspensionwhose solids concentration is in the range of 1-15% by weight andpreferably 3-10% by weight is produced in the associated stirred tank.It is ensured that the density of the liquid phase of the suspension inthe first separating stage is set to a value which is between thehighest and second-highest density of the principal components of thecarpet. In the second separating stage, the density of the liquid phaseis between the lowest and the second-lowest density of the principalcomponents of the carpet. The carpet component with the highest specificgravity is normally, due to the filler, the carpet backing material,with a density of about 1.5-3.5 kg per liter. The second-heaviestcomponent is formed by the pile fibers, with a density of about 1.35 kgper liter for polyester and about 1.15 kg per liter for polyamide.Correspondingly, for example, the density of the liquid phase of thesuspension in the first separating stage in the case of recovery ofpolyester fibers is set to a value in the range from about 1.36 to about1.5 kg per liter and in the case of polyamides in the range from 1.16 to1.3 kg per liter (at 20° C.). The separating salt used here plays animportant role in setting the density of the first suspension. In thesecond stirred tank, the setting of the pH in the range 2-6 by additionof acid is also of importance in addition to the density. The additionof small amounts of less than 0.2 g per liter of a commerciallyavailable wetting agent and/or antifoam agent to the first and/or secondstirred tank is advisable.

[0006] Particularly good separation results are achieved with thedouble-cone full-jacket screw centrifuge. With this commerciallyavailable apparatus, it is possible to separate the fraction of thesolid having a higher density than the liquid phase from the fractionhaving a lower density than the liquid phase and to obtain a liquidphase as the third phase. The two solid phases are discharged with aresidual moisture content in the range from 2 to 25% by weight,depending on the consistency of the particles. The heaviest solidfraction obtained in the first separating stage usually consistsprincipally of mineral fillers, for example synthetic rubber to whichchalk has been added, and contains only small amounts of fiber material.After drying, this fraction can be passed to thermal energy recovery ormaterial recycling.

[0007] A refinement of the invention consists in that the polymer fibermaterial of the comminuted carpet pieces consists at least partly ofpolyamide fiber material, and in that the second high-solids phase,calculated in dry form, consists of at least 50% by weight of polyamidefiber material. A polymer fiber material-rich phase which consists of atleast 90% by weight of polyamide fiber material is preferably withdrawnfrom the second separating stage. This polyamide fiber material can bere-used without difficulties, since it has the requisite purity for use,for example, as raw material in recycling methods.

[0008] Embodiments of the process are explained with the aid of thedrawing, which shows a flow chart of the process.

[0009] The carpet waste to be processed is fed, on transport route (1),firstly to a precomminution step (2), for example a shredder. Thepre-comminuted material then passes either on transport route (2 a) to ahammer mill (3) or on transport route (2 b) directly to fine comminutionin a cutting mill (5). The carpet material passing through the hammermill (3), which is usually soiled to a relatively great extent, ispassed through line (6) to a sieve (7), which has mesh widthsapproximately in the range of 3-10 mm. The dirt adhering to the carpetis separated off together with a fraction of chalk and removed throughline (8), and the carpet pieces pass on route (7 a) to the cutting mill(5). The route via the hammer mill (3) and the sieve (7) has theadvantage that wear-promoting dirt, for example sand, is removed beforeentry into the fine comminution step. Furthermore, the material flowcoming from the shredder (2) is reduced. This enables subsequent plantparts to be built smaller, and subsequent losses of salt and water whichoccur via the residual moisture content of the solids are reduced.

[0010] The discharge from the cutting mill takes place via a perforatedplate with holes approximately in the range of about 3-10 mm, preferably4-8 mm. Due to the comminution, substantially complete separation of thecarpet composite takes place. The comminution can be carried out eitherin dry or wet form, depending on the degree of soiling of the rawmaterial. In the latter case, water is supplied through line (5 a) andsoiled water is discharged through line (5 b).

[0011] Comminuted carpet material having piece sizes approximately inthe range of 3-20 mm is passed through line (9) to a first stirred tank(10), to which a first aqueous solution containing separating salt isalso added through line (11). A first liquid phase which is fed back islikewise introduced into tank (10) through line (12). A first suspensionis produced, which is fed to a first separating stage (14) through line(13). The first suspension has a solids content of usually 1-15% byweight, and the density of the liquid phase in the case of recovery ofpolyamide fiber material is usually in the range of 1.16-1.2 kg perliter.

[0012] From the first separating stage (14), a first high-solids phase,which is the heavy phase containing rubber and chalk, is withdrawnthrough line (16). The second high-solids phase, which contains thepolymer fiber material to be recovered, is withdrawn in line (17) andintroduced into a second stirred tank (20). The liquid phase likewiseformed in the first separating stage is fed back in line (12).

[0013] An aqueous, acid-containing separation solution is fed to thesecond tank (20) through line (21), and a recycled liquid phase comingfrom line (22) is also introduced into tank (20). The acid is strongerthan H₂CO₃ in order that it readily dissolves chalk in particular. Asuspension whose liquid has a pH of 2-6, so that, inter alia, all thecalcium compounds dissolve, is produced in tank (20). The suspensionproduced passes through line (24) with a solids content of 1-15% byweight into the second separating stage (25), which, like the firstseparating stage (14), can be a double-cone full-jacket centrifuge. Thedensity of the liquid in the suspension in line (24) is usually 1.0-1.12kg per liter in the case of the recovery of polyamide fiber material.The heavier high-solids phase, which usually consists of pile fibers, iswithdrawn from the second separating stage through line (26). Thismaterial can be fed to a depolymerization plant. The desired, polymerfiber material-rich phase, which may consist, for example, of at least90% by weight of polyamide fibers, is obtained in line (27). The liquidphase likewise separated off is partly fed back in line (22), and acertain proportion thereof can be removed from the process through line(28) and fed to purification (30), for example a thickener. Purifiedaqueous separation solution is fed back in line (31). The soiled waterformed in line (5 b) can also be introduced into the thickener (30).

EXAMPLE 1

[0014] Use is made of a plant corresponding to the drawing, to which arefed 50 kg of carpet having the following composition through transportroute (1): Pile material comprising polyamide fibers (PA) 35% by weightPolypropylene as backing fabric (PP)  7% by weight Foam backing ofchalk-containing styrene-butadiene 55% by weight latex (SBR) Dirt  3% byweight

[0015] The carpet is pre-comminuted in a shredder (2) fitted with a 90mm sieve. The dirt adhering to the pieces and other fine fraction aresubsequently mechanically loosened by means of a hammer mill (3). Thecarpet is passed via transport route (6) to the sieving machine (7).This separation device is fitted with a sieve having a mesh width of 5mm. 2.6 kg of dirt and other fine fraction are separated off from theunderflow.

[0016] The shredded carpet from the top flow of the sieving machine ispassed to the cutting mill (5), which is fitted with a perforated platehaving square holes with a diameter of 6 mm. The carpet is finelycomminuted in dry form in this device. The ground carpet is passed vialine (9) to the stirred tank (10). The tank contains 900 kg of aseparation solution set to a density of 1.17 kg/l by means of Ca(NO₃)₂,some of which has been initially introduced via line (12). In order toset the density, the solution contains 194 kg of Ca(NO₃)₂. Thesuspension prepared is passed via line (13) to a double-cone full-jacketscrew centrifuge (14).

[0017] The first high-solids phase (dry weight: 26.2 kg) is dischargedwith a residual moisture content of 22% by weight through line (16) andthe second high-solids phase (dry weight: 21.1 kg) is discharged with aresidual moisture content of 12% by weight through line (17), and theseparation solution (12) is fed back into the stirred tank (10). Thesecond high-solids phase is introduced into the second stirred tank (20)and suspended in 399 kg of water. 2.4 kg of nitric acid (21) having aconcentration of 50% are added to the suspension prepared in the stirredtank (20), to give a pH of 4.

[0018] The suspension prepared is introduced into the second separatingstage (25) via line (24). The third high-solids phase (dry 4.7 kg) isdischarged with a residual moisture content of 14% by weight throughline (27), and the fourth high-solids phase (dry 16.4) is dischargedwith a residual moisture content of 16% by weight through line (26). Theseparation solution (22) is partly fed back into the stirred tank (20),and a sub-stream (28) of 40 kg is removed and fed to the thickener (30).After clarification and removal of 0.1 kg of impurities, re-introductioninto the separation circuit in the 2nd stage (line (31)) takes place.

[0019] The individual high-solids phases have the following composition,based on the dry matter: PA PP SBR Dirt First high-solids phase  3.4% bywt.  0.1% by wt. 94.8% by wt.  1.7% by wt. Second high-solids phase77.8% by wt. 16.2% by wt.  5.9% by wt.  0.1% by wt. Third high-solidsphase  8.7% by wt. 90.3% by wt.  1.0% by wt.  0.0% by wt. Fourthhigh-solids phase 98.2% by wt.  0.2% by wt.  1.5% by wt.  0.1% by wt.Sieve residue  6.6% by wt.  1.3% by wt. 52.2% by wt. 39.8% by wt.

EXAMPLE 2

[0020] Use is likewise made of a plant corresponding to the drawings towhich 50 kg of carpet having the following composition are fed throughtransport route (1): Pile material comprising polyamide fibers (PA) 35%by weight Polypropylene as backing fabric (PP)  7% by weight Foambacking of chalk-containing styrene-butadiene 57% by weight latex (SBR)Dirt  1% by weight

[0021] The carpet is pre-comminuted in a shredder (2) as in Example 1.The shredded carpet is subsequently passed via line (2 b) to the cuttingmill (5). The cutting mill is fitted with a perforated plate havingsquare holes with a diameter of 6 mm. The carpet is finely comminuted inthis device with addition of 200 kg of water. 150 kg of water and 1.0 kgof dirt are discharged from the mill and fed via line (5 b) to thethickener (30). 50 kg of water remaining in the raw material are fed tothe stirred tank (10) together with the ground carpet via line (9). Aseparation solution prepared by means of Ca(NO₃)₂ is initiallyintroduced into the tank via line (12) and is set to the density 1.17kg/l by means of the 50 kg of water introduced from the mill, giving atotal amount of 931 kg of separation solution. In order to set thedensity, the solution contains 201 kg of Ca(NO₃)₂. The suspensionprepared is fed via line (13) to a double-cone full-jacket screwcentrifuge (14). The first high-solids phase (dry weight: 27.8 kg) iswithdrawn with a residual moisture content of 22% by weight through line(16), and the second high-solids phase (dry weight: 21.2 kg) isintroduced with a residual moisture content of 12% by weight throughline (17) into the second stirred tank (20), where it is suspended in400 kg of water. The separation solution from line (12) is fed back intothe stirred tank (10).

[0022] 2.6 kg of nitric acid having a concentration of 50% are added tothe suspension prepared in the stirred tank (20), and the pH is set to3.5. The suspension prepared is introduced into the second separatingstage (25) via line (24). The third high-solids phase (dry 4.8 kg) isdischarged with a residual moisture content of 14% by weight into line(27), and the fourth high-solids phase (dry 16.4) is withdrawn with aresidual moisture content of 16% by weight in line (26).

[0023] The separation solution (22) is fed back into the stirred tank(20). A sub-stream (28) of 40 kg is removed and fed to the thickener(30). After clarification and removal of 1.1 kg of impurities,re-introduction into the separation circuit in the 2nd stage takes placethrough line (31). To this is added 150 kg of water, introduced into thethickener through line (5 b).

[0024] The individual high-solids phases have the following composition,based on the dry matter: PA PP SBR Dirt First high-solids phase  3.2% bywt.  0.1% by wt. 95.9% by wt. 0.7% by wt. Second high-solids phase 77.5%by wt. 16.2% by wt.  6.3% by wt. 0.0% by wt. Third high-solids phase 8.7% by wt. 90.2% by wt.  1.1% by wt. 0.0% by wt. Fourth high-solidsphase 98.2% by wt.  0.2% by wt.  1.6% by wt. 0.0% by wt.

1. Process for separating polymer fiber material from comminuted carpetpieces, which are fed to a first stirred tank together with an aqueoussolution containing separating salt, and a first suspension is withdrawnfrom the first stirred tank and fed to a first mechanical separatingstage, from which a first high-solids phase, a second high-solids phasecontaining polymer fiber material, and a liquid phase are separated off,the second high-solids phase being mixed with a water-containingseparation solution in a second stirred tank, and a second suspensionbeing withdrawn from the second stirred tank and fed to a second,mechanical separating stage, from which a third high-solids phase, apolymer fiber material-rich phase, and a liquid phase are separated off,characterized in that an acid which is stronger than H₂CO₃ is introducedinto the second stirred tank together with the water-containingseparation solution, and the pH of the liquid in the second stirred tankis adjusted to 2-6.
 2. Process according to claim 1, characterized inthat the separating salt fed to the first stirred tank is a calcium saltwhose acid displaces calcium carbonate.
 3. Process according to claim 1or 2, characterized in that the polymer fiber material of the comminutedcarpet pieces consists at least partly of polyamide fiber material, inthat the second high-solids phase, calculated in dry form, consists ofat least 50% by weight of polyamide fiber material, and in that thepolymer fiber material-rich phase coming from the second mechanicalseparating stage consists of at least 90% by weight of polyamide fibermaterial.
 4. Process according to claim 1 or one of the followingclaims, characterized in that the carpet pieces to be processed comefrom dry comminution or wet comminution.